Internal redox reactions

Stannous Sulfate. Stannous sulfate (tin(Il) sulfate), mol wt 214.75, SnSO, is a white crystalline powder which decomposes above 360°C. Because of internal redox reactions and a residue of acid moisture, the commercial product tends to discolor and degrade at ca 60°C. It is soluble in concentrated sulfuric acid and in water (330 g/L at 25°C). The solubihty in sulfuric acid solutions decreases as the concentration of free sulfuric acid increases. Stannous sulfate can be prepared from the reaction of excess sulfuric acid (specific gravity 1.53) and granulated tin for several days at 100°C until the reaction has ceased. Stannous sulfate is extracted with water and the aqueous solution evaporates in vacuo. Methanol is used to remove excess acid. It is also prepared by reaction of stannous oxide and sulfuric acid and by the direct electrolysis of high grade tin metal in sulfuric acid solutions of moderate strength in cells with anion-exchange membranes (36). 

This is an typical example of a dicarboxylic acid in that C-C cleavage is the only route for oxidation. No study of the Co(III) oxidation has been made although it is highly probable that reaction would proceed through an oxalate complex. The thermal decomposition of Co(Ox)3 has been shown to be a first-order process and probably involves an internal redox reaction, viz. 

This compound breaks down to [Co(CN)5H20] and [(CN)5CoOC5H40H] . The latter in turn undergoes an internal redox reaction to give [Co(CN)5H20] and hydroquinone. Both first-order steps show general acid catalysis. 

Illustrated in Scheme 7.8 are the mechanisms that give rise to the products shown in Scheme 7.7. These mechanisms involve either electrophilic attack or an internal redox reaction. The internal redox reaction shown in Scheme 7.8 involves proton trapping from the solvent or from the hydroquinone hydroxyl group as shown. This process has been documented for the mitomycin system50 and also occurs in many quinone methide systems.25,30,31... 

The toxicity of 3-methylindole has been attributed to methyleneindolenine trapping of nitrogen and sulfur nucleophiles.57 60-62 Likewise, the ene-imine shown in Scheme 7.9 readily reacted with hydroquinone nucleophiles, resulting in head-to-tail products. Shown in Fig. 7.6 is the 13C-NMR spectrum of a 13C-labeled ene-imine generated by reductive activation. The presence of the methylene center of the ene-imine is apparent at 98 ppm, along with starting material at 58 ppm and an internal redox reaction product at 18 ppm. Thus, the reactive ene-imine actually builds up in solution and can be used as a synthetic reagent. 

Reductive activation of the quinone shown in Scheme 7.9 and incubation in methanol afforded a complex mixture of products consisting mainly of head-to-tail coupling at C-5 or C-7 (Scheme 7.10). Minor reactions involve transfer of H2 from the hydroquinone to the ene-imine (internal redox reaction) and methanol trapping. The structures of the dimers and trimers in Scheme 7.10 were derived from H-NMR,... 

The process that affords the alkenes with13 C = 45 ppm is essentially an internal redox reaction wherein electrons flow from the fused tetrahydropyrido ring to the quinone ring by means of a series of tautomerizations. 

The reductive coupling of allyl halides to 1,5-hexadiene at glassy C electrodes was catalyzed by tris(2, 2,-bipyridyl)cobalt(II) and tris(4,4 -dimethyl-2, 2/-bipyridyl)cobalt(II) in aqueous solutions of 0.1 M sodium dodecylsulfate (SDS) or 0.1 M cetyltrimethylammonium bromide (CTAB).48 An organocobalt(I) intermediate was observed by its separate voltammetric reduction peak in each system studied. This intermediate undergoes an internal redox reaction to form 1,5-hexadiene... 

It explodes at temperatures around 150°C. Thermal decomposition appears to involve an internal redox reaction in the anion leading to formation of trichloro(chlorato)oxostannate(IV). 

The complex anion [Pt(S-Me2SO)Cl3] undergoes an internal redox reaction in acidic media, and evidence for the formation of Pt(IV) species and Me2S has been presented (466). This may be an explanation for the deoxygenation of (CH2)4SO previously mentioned (164). The oxidation of Pt(II) to Pt(IV) with concomitant reduction of Me2SO to Me2S has been accomplished using hydrochloric acid (357), as shown in Eq. (28). 

Picryl chloride (87) reacts with hydroxylamine hydrochloride to yield 2,4,6-trinitroaniline (53) (picramide) and not the expected At-hydroxy-2,4,6-trinitroaniline. In contrast, the same reaction in the presence of sodium ethoxide is reported to yield 4,6-dinitrobenzofuroxan (94) via substitution of the halogen by hydroxylamine, followed by an internal redox reaction between the hydroxyamino group and one of the adjacent o-nitro groups. ... 

Concurrently with Bode s work, Rovis and co-workers reported an internal redox reaction of a-haloaldehydes to provide a variety of esters in good yields [110]. Triazolium salt 177 proved most effective for the transformation of... 

Bode and co-workers have shown that the outcome of internal redox reactions is uniquely dependent on the base [111]. When diisopropylethyl amine is used in the reaction of an enol and an alcohol, the initially generated homoenolate is protonated... 

Ligands such as aniline (an), 1,2-diaminobenzene (dab, o-phenylenediamine) and 2,2 -dia-minobiphenyl886 887 are classed separately, not because their ability to bind to a central metal is any less than the ligands discussed previously, but because of their potential non-innocent behavior888 with respect to internal redox reactions. Indeed, the dark blue complex isolated from the air oxidation of Con/dab in aqueous ethanol (a conventional route to yellow Co(diamine)3+ systems) has been shown to have structure (117) with five-coordinate Co11.888 Related diimine complexes have been reported for Ni11889 as well as the conventional Ni(dab)(+,890 Co(dab)3+ 891 and Pt(dab) + 892 systems. 

Ketones can be reduced directly to alkanes by the Wolff-Kishner reduction. In this reduction, the ketone is converted to the hydrazone, which is treated in situ with sodium hydroxide. An internal redox reaction occurs in which the carbon is reduced and the hydrazine is oxidized to nitrogen. The best experimental conditions include the use of NaOH and ediylene glycol as solvent to carry out the reduction. 

Complicated internal redox reactions occur when atomic H is involved as a reducing agent. In quartz where the reduction of Ti4+ has been attributed to reactions with atomic H (21) Ti4+ + H + 02" = Ti3+ + OH , atomic H is stable only at low temperature (1). In brazilianites H may be responsible for the reduction of Fe3+ to Fe2+ plus OH (12.). Because H easily combines to H2 it becomes unreactive or escapes. The irreversibility of the redox reaction in brazilianites may be due to loss of H2. 

The butyl derivative - but not the phenyl derivative - undergoes an internal redox reaction below 20° to form dibutyl ditellurium and disulfide anion2. 

The lithium alkyltelluroselenolates undergo internal redox reactions below room temperature to form dialkyl ditellurium and the diselenide anion. The phenyl derivative is stable under these conditions2. 

Protonation by acid-base chemistry leads to an internal redox reaction (Fig. 11.19), without change of the number of electrons (Heeger, 2001 MacDiarmic, 2001). The semiconductor (emeraldine base, emeraldine salt, 100 S/cm). Complete protonation of the imine nitrogen atoms in emeraldine base by aqueous HC1 results in the formation of a delocalised polysemiquinone radical cation. This is accompanied by an increase in conductivity of more than 12 orders of magnitude. 

The lipoxygenase family of enzymes catalyse stereospecific oxygenation reactions of fatty-acid substrates. The active site incorporates a non-haem iron centre in as yet an unidentified environment. The active form of the enzyme is the iron(III) state but is converted to iron(II) as the fatty acid is oxidised [91]. Catechol-containing compounds inhibit these enzymes by forming a ternary complex with the iron centre and depending on the substituents on the catechol moiety may even facilitate an internal redox reaction leading to the formation of iron(II) and an inactive form of the enzyme [92,93]. 

Reynolds NT, Read de Alaniz J, Rovis T (2004) Conversion of a-haloaldehydes into acylating agents by an internal redox reaction catalyzed by nucleophilic carbenes. J Am Chem Soc 126 9518-9519... 

Mass spectral data for [RuL3] (HL = RC(0)CH2C(0)R, R = R = Me, CF3 R = Me, R = CF3) suggest relatively little tendency for internal redox reactions in these complexes.2056 Several studies on the electrochemistry of tris ketoenolate complexes have been publish-e(j 2052,2055,2062,2064,2079 [Ru(acac)3] shows a one electron redox couple to [Ru(acac)3] at E, = —0.72 V and —0.51 V vs. SCE in MeCN and H20 respectively.2079 The effect of substitution on acac on the Ru1,1/U redox couples for the corresponding complexes has been assessed and related to the redox couples [Ru(NH3)6]2+/3+, [Ru(en)3]2+/3+ and [Ru(CN)6]3-/4 , 2055 A linear relationship was observed between Ei values for the RuIV 11,n couples and the sum of the Hammett constants for the functionalities on the coordinated ketoenolate.2052 Association between [RuL3] and alkali metal ions has been noted 2052 the rate of aquation of [Ru(acac)3] was found to be relatively slow, with a rate constant k < 1 x 102M-1 s-1. 2078 H[Ru(acac)3] is observed to be a relatively strong acid with pKa < 3.5.2078... 

---